Japanese Patent Abstract 11121546A2 “Capillary-holding structure of ultrasonic horn” describes a capillary held in a slotted aperture which is clamped around the capillary by a transverse bolt fitted through a washer and screwed into a nut.
The mass of the transducer horn in this prior art arrangement is unbalanced due to the head of the bolt lying on one side of the transducer tip. This imbalance causes the transducer tip to twist dr sway as it is advanced toward the bonding site.
U.S. Pat. No. 5,180,093 “Apparatus for ultrasonic bonding” describes a bonding tool carried in a passage in the tip of an ultrasonic transducer. A threaded set screw at the tip forces the tool against edges and flat surfaces in the passage to secure the tool to the transducer. This arrangement does not provide an efficient transfer of ultrasonic energy due to the small area of contact between the transducer and the tool.
In both the prior art arrangements cited above, the transducer capillary or tool experiences a reduced vibration amplitude at ultrasonic frequencies due to the additional mass of the mounting screw and associated hardware which absorbs kinetic energy for its motion.
Also, the additional mass of the clamping hardware at the tip of the transducer drastically reduces the low frequency resonance of the tip (i.e. below 2000 Hz) by at least 100 Hz, reduces the resonant frequency at the ultrasonic frequency range and increases the impedance of crystals in the ultrasonic transducer.
Furthermore, arrangements requiring adjustment of a threaded screw to tighten the tool or capillary mounting suffer from variation in clamping force at the tool-horn interface due to human error or normal variation in the tightening torque applied by production technicians.
Still further, systems using a threaded fastener suffer, over time, from wear of the thread and the threaded hole into which it is fitted, causing further deterioration in transfer of energy and difficulties in applying the correct torque to provide consistent tightening of the tool to the horn.
U.S. Pat. No. 6,422,448 “Ultrasonic horn for a bonding apparatus” describes a capillary mounted in a hole in an ultrasonic horn. The capillary hole communicates with a parallel second hole by way of a slot. A non-circular jig temporarily inserted into the second hole is rotated to widen the capillary hole allowing insertion or removal of a capillary tool. Upon a second rotation of the jig, the capillary hole returns toward its original size to grip the capillary. This provides a more repeatable attachment of the capillary to the transducer, than systems requiring adjustment of a threaded bolt or screw. However, the insertion of the jig from above, and the rotation of the jig to manipulate the size of the capillary hole, can apply undesirable forces to the Z-axis assembly of the bonding apparatus.